This didn't work for Steve Jobs
The best way of doing this, based on years of science, would be, well, to eat nothing for 24+ hours at a time, but make sure you stay hydrated; as in, actually fast. The second best would be to seriously curb your carbs, under 30g a day; also tied for second best is to eat just once a day, none of this unscientific three square meals hogwash.
Three of these together could halt the progress of some cancers, and before the shitstorm that was 2020, scientists were publishing papers involving animal models on this.
Steve Jobs did none of these, and was, sadly, off in la-la land when someone with his money and connections could have had access to next generation scientifically-based treatments. Fruitarianism is, frankly, dangerous.
So water and coffee or tea (without milk, of course) would be fine. You're trying to avoid an insulin response and firing up the entire machinery of digestion.
I think it's non-controversial to say that this starves the cancer cells.
Perhaps less certainly we can also say that digestion demands a lot of resources and is an interrupt for a lot of other processes. When your body has nothing to do for 24-36 hours eventually lower priority tasks get attended to ... like garbage collection.
Jobs had GEP-NET cancer, which have 5 years OSR of 70% at stage IV. It's a slow growing cancer, very survivable and even surgically curable in early stage.
The fast, almost always fatal is the pancreatic adenocarcinoma.
Also, the mortality rate of a cancer is a function of many variables (stage at the time of diagnosis, tumor differentiation, tumor location, etc.). A number like 95% doesn't make any sense without a lot of context.